1. Field of the Invention
The present invention relates to a fuel cell, specifically, to a fuel cell that stably generates electricity mainly in a mixed gas of fuel gas and air.
2. Description of the Related Art
Planar type (stack-type), tubular type (tube-type) and other types of cell designs have been conventionally proposed for fuel cells.
As disclosed in Japanese Unexamined Patent Publication No. 1993-3045, a planar type cell comprises a fuel electrode and an air electrode disposed on the front and back surfaces, respectively, of a flat electrolyte. The thus formed cells are used in a condition where a plurality of cells are laminated having a separator between adjacent cells. The separator completely separates the fuel gas supplied to each cell from the air, and a gas seal is provided between each cell and separator. However, in this planar type cell, because the gas seal is provided by applying pressure to the constituent components of the cell, the cell is easily damaged by oscillation, heat cycles, etc. This poses a significant problem in bringing the fuel cell to practical use.
In contrast, the tubular type cell disclosed in, for example, Japanese Unexamined Patent Publication No. 1993-94830, comprises a fuel electrode and an air electrode disposed on the outer surface and inner surface, respectively, of the cylindrical electrolyte. Among tubular type cells, vertical-stripe-type and horizontal-stripe-type fuel cells have been proposed. Although a tubular type fuel cell is advantageous in having excellent gas-sealing properties, its manufacturing process is complicated because its construction is more complex than that of a planar type cell and this makes the manufacturing cost thereof high.
Furthermore, these cell designs have the following drawbacks: Both in planar type cells and tubular type cells, the electrolyte needs to be made thin to improve their performance, and the ohmic resistance of the electrolyte material needs to be reduced. However, unduly thin electrolyte lacks sufficient strength and decreases the vibration resistance and durability of the cell.
For this reason, a non-diaphragm-type solid oxide fuel cell has been proposed to take the place of the above-mentioned planar type and tubular type fuel cells, wherein, as disclosed in, for example, Japanese Unexamined Patent Publication No. 1996-264195, a fuel electrode and an air electrode are arranged on the same surface of a substrate formed of a solid electrolyte, and electricity is generated by supplying a mixed gas of fuel and air thereto to conduct ions mainly on the surface of the electrolyte. Because fuel and air do not need to be separated in this fuel cell, the separator and gas seal become unnecessary, and the construction thereof can be significantly simplified.
As described above, in the fuel cell disclosed in Japanese Unexamined Patent Publication No. 1996-264195, an electrolyte is used as a substrate and a plurality of fuel electrodes and air electrodes are disposed on a single surface thereof. However, because, in the electrolyte, the portion necessary for cell reaction is in the vicinity of the electrodes, there are many portions that do not contribute to the cell reaction in the electrolyte used as the substrate. Because the materials for electrolytes are not inexpensive, when portions exist that do not contribute to the cell reaction, the cost performance is undesirably lowered.
The present invention aims to solve the above problems, and to provide a fuel cell that is capable of improving cost performance without lowering its cell performance.